1. Field of the Invention
The present invention relates to a variable square-wave drive device for use in camera modules such as an HHP (Hand Held Phone), and more particularly to a variable square-wave drive device for controlling square waves using a feedback- or bias-control method to vary the square waves, such that it can correctly control a curvature of an LL (Liquid Lens), and can more precisely and stably control focus and zoom functions of a camera module.
2. Description of the Related Art
Typically, two different liquids are contained in a transparent body of an LL, and individual curvatures of the liquids can be adjusted by a driving voltage, such that it is well known in the art that the focus and zoom functions of the camera module can be controlled without using additional mechanical mechanisms.
Optical devices using liquid crystal lens have been disclosed in U.S. Pat. Nos. 4,190,330 and 6,433,770, which are incorporated herein by reference.
The liquid lens disclosed in U.S. Pat. No. 4,190,330 is shown in FIG. 1.
FIG. 1 is an exploded perspective view illustrating a conventional liquid lens. Referring to FIG. 1, the liquid lens includes a transparent substrate 13 and a polarizer 11 having optically transparent-coated concave surfaces to be installed facing each other, and an electrical conductive electrode 14 coated with a liquid crystal array layer 15. The polarizer 11 is aligned in an X-axis direction of each director of a liquid crystal material contained in the array layer 15's space. The electrode 14 is connected to a voltage generator 16, such that an electric field induced by the voltage generator 16 is generated between the electrodes 14.
As the electric field intensity between the electrodes 14 gradually increases, the liquid crystal material's director moves to a Z-axis direction by a predetermined length directly associated with the electric field intensity.
Many developers have recently conducted intensive research into a variety of devices for driving such liquid crystal lens, and a representative drive circuit disclosed in U.S. Pat. No. 6,433,770 is shown in FIG. 2.
Referring to FIG. 2, the drive circuit includes a detector 1 for detecting an optical signal, a filter/buffer unit 2 for filtering an output signal of the detector 1, and an oscillator 3 for generating a predetermined frequency, and controlling a duty cycle of the predetermined frequency according to a control signal of the filter/buffer unit 2.
The aforementioned conventional drive circuit varies optical density in response to peripheral optical signals, such that it can constantly adjust a brightness or luminance of a liquid lens.
However, the aforementioned conventional liquid crystal lens drive circuit cannot control a curvature of the LL, such that it is also unable to perform a focus control function capable of being carried out using such a curvature control function.
In conclusion, the conventional LL drive circuit must control the LL's curvature, and further, must more correctly control the LL's curvature.